I've been trying to get the official Sierra mods to add new player models working:

https://www.moddb.com/games/swat-3/addons/sierras-swat-3-tgoty-mod-1-male-swat

https://www.moddb.com/games/swat-3/addons/sierras-swat-3-tgoty-mod-5-female-tango

https://www.moddb.com/games/swat-3/addons/sierras-swat-3-tgoty-mod-2-female-swat

https://www.moddb.com/games/swat-3/addons/sierras-swat-3-tgoty-mod-3-agent-pack

However the models appear the same in-game. any help?

Make sure the game is not running.

You copied the .zip files into the 'Mods' folder? The Mods folder should be found where you installed Swat 3.

Do not unzip the mods.

Use the mod manager to turn on these mods.

Start the game.